Fix a typo error in the openvz image link

It's a -, not a ..

Change-Id: I05a39e20234d89c08cff66b57f6b350ad0fe4a98
diff --git a/stackrc b/stackrc
index 3e93d23..36171cc 100644
--- a/stackrc
+++ b/stackrc
@@ -224,7 +224,7 @@
 case "$VIRT_DRIVER" in
     openvz)
         DEFAULT_IMAGE_NAME=${DEFAULT_IMAGE_NAME:-ubuntu-12.04-x86_64}
-        IMAGE_URLS=${IMAGE_URLS:-"http://download.openvz.org/template/precreated/ubuntu-12.04.x86_64.tar.gz"};;
+        IMAGE_URLS=${IMAGE_URLS:-"http://download.openvz.org/template/precreated/ubuntu-12.04-x86_64.tar.gz"};;
     libvirt)
         case "$LIBVIRT_TYPE" in
             lxc) # the cirros root disk in the uec tarball is empty, so it will not work for lxc